This project involves performing studies directed towards the development of vaccines using recombinant DNA technology to synthesize immunogenic peptides from microbial agents. The objective is to identify specific natural or genetically modified proteins which when used as immunogens will protect against challenge by Bordetella pertussis, the causative agent of whooping cough. These antigens will then be considered for use in a new generation component vaccine. We are presently working on pertussis toxin, a protein consisting of five subunits, which is a major protective immunogen in whooping cough vaccines. Our initial effort involves evaluating individual subunits of pertussis toxin produced synthetically using recombinant DNA technology. Our earliest results suggested that the standard mouse lethal intracerebral challenge (ic) model was incapable of reliably identifying protective pertussis components and was variably reliable in demonstrating protection with a commercially available whole cell vaccine. By modifying the ic challenge to include a small dose of active pertussis toxin, which is incapable of stimulating immunoprotection when administered alone, we have been able to consistently demonstrate protection following immunization with both purified components and recombinant component subunits. In the 31 experimental groups studied so far, the first 15 did not utilize active pertussis toxin. In those experiments, immunization with recombinant pertussis toxin subunits S1 and S2 produced in E. coli did not yield protection which was greater than that provided by vehicle alone. Following inclusion of active toxin in the protocol, immunoprotection by S1 and S2 reached 70% of the level provided by the whole cell vaccine which served as a positive control. Deletion and substitution mutants of the S1 subunit are currently being tested to identify the epitopes associated with protection from lethal challenge. In addition, S1 based peptides are being synthesized to test their protective potential.